Blasting device



"sept, 1'6, 1941. J.. TAYLOR 2,256,298

v BLASTING DEVICE v Filed OG'C. 27, 1957 MMF-...J

James Taylor INVENToR.

ATTORNEY Patented Sept. 16, 1941 '2,256,298 l l l LAsrINc DEVICE JamesTaylor, Saltcoats, Scotland, assgnor to Imperial Chemical IndustriesLimited, a corporation of Great Britain Application October 27, 1937,Serial No. 171,391

In Great Britain October 29, 1936 claims.

.This invention relates to blasting devices, par- Vticularly to those ofthe kind comprising a pres" sure-resistance reutilisable container, acharge of a solid material capable of undergoing a non- Vdetonatingvgas-evolving decomposition when locallyl initiated, `and'means forlocally initiating the decomposition of the said charge.

Blasting devices of this kind have been proposed in which the containeris charged at atmospheric pressure with a solid material of thekinddescribedvand is tted with avvalve or rupturable disc seal of hightensile strength material adapted to release the products ofdecomposition ofthe charge when the internal pressure has attained a"predetermined and considerable value sufficient to produce a blastingleffect when the device has been suitably located in a borehole.

Blasting devices of this latter kind rhave beenvr` .compositions is thattheir rates of exothermic decomposition, and hence their rates ofdevelopment of gas pressure ywhen confined, do notv become great enoughto produce a blasting efl fect until the decomposition is taking placeunder an already considerable pressure. This property is desirable inthat the unconfined compositions may be handled with safety; buthithertothey have not been considered suitable for use as blastingexplosives, except when in proper associationy with a pressure-resistantventing container, since if they are loosely tamped in a borehole, or ifthe borehole has breaks or fissures, any gas pressure developed by theirinitial decomposition will leak away too rapidly for the completedecomposition of' the charge to produce an eiective blast.

In the devices used hitherto, in which the charged container is adaptedto vent when the y internal pressure reaches a value lsuitable forblasting, the considerable pressure mentioned above is built up by thegas evolved during the relatively slow decomposition of the charge imimediately after its initiation at substantially norprolonged time staticpressures up to the venting pressure.

The provision of a release valve'or of view of economy and simplicity,but also with a view to a more efficient use of the energy of dischargeof the gases and the elimination of deterioration of the apparatus dueto erosion at the venting end of the device.

This invention has as an object to provide a blasting device which doesnot require any screwed unions or detachable venting cap. A

further object is to provide a blasting device L which shall bemore'simple and economical than known'blasting devices. Further objectswill appear hereinafter.

These objects are accomplished by the-follow` ing invention. lI havevfound vthat blasting de-` .vices of the kind venting at a predeterminedarid considerable pressure may be constructed, without any necessity forthe provision of a seal of which the materialis capableY of prolongedresistance to pressures less than the Venting pressure, by lmaking useof 'the pressure-resisting properties of a column'of granular or likematerial supported in a rigid tube, if adequate support is given to thecolumn' of granularA material within a pressure-resistant tube,preferably byra gas-tight supporting and sealing member. The supportneed only withstand a static pressure that is small relative to thepressure at which the container is intended to vent, al-

though it must be capable of withstanding presn sure substantiallyvgreater than atmospheric. Thus for example the support alone must bevcapable of withstanding an internal pressure of square inch. When suchsupport is used in conjunction with a column 4of sand thatis shortrelative 'to the length of sand tamping hitherto employed with safetyexplosives to ensure a safe blast in a dangerous atmosphere, theassembly can withstand pressures exceeding 30tons per square inch.

Referring generally .to the drawing there is depicted therein a view invertical cross-section of a blasting device according to thepresentninvention. y

In greater detail theicylindrical steel tube l is depicted as closed atone end. Adjacent to said closed end is a charge 2 of sodium nitrite lEmbedded in said Y and ammonium chloride. charge is an electric igniter3, the leadsv 4 of which pass downward and out through `the otherk endof said steel tube. Belowl the aforesaid charge 2 is a column of sand 5supported by a plaster of Paris plug l retained inplace by means Aquiredin each case to dislodge the assembly from the tube is given in thefollowing table. The pressure required to dislodge the plaster of Parisplug alone was approximately-V2 ton per square inch.

Heght of Breakdown sand pressure column Tana per Inches square inch 1 0.53 Z 0. 87 3 4. 07 3% 1l. 7 4 14Y 5 The usual'venting pressure of a11/4" internal diameter blasting device of the kind described is 12 tonsper square inch.

According to the present invention, a blasting device comprises apressure-resistant reutilisable container provided with a seal adaptedto yield under an internal pressure substantially higher thanatmospheric pressure, but considerably less than the pressure at whichthe device is intended to vent; a charge of a solid material capable ofundergoing a non-detonating gas-producing exothermic decomposition afterbeing locally initiated; means for local initiation of the charge; and aquantity of a granular or like substance having the property of packingunder pressure, completely lling the free space between the charge andthe seal, and in amount such that the device vents at a pressuresuiicient to exert a blasting effect, but insuilicient to cause anydeformation or other damage to the container. The actual magnitude ofthe venting pressure will be a function of the length of the column ofsand or like granular material; and it will be under- Weight of Lengthof Length of Maximum charge tube sand pressure Tous per Grams InchesInches square meh 150 17 t-8 12 30 12-15 l5 200 l5 2-4 855 20 -S 12 2512-14 15 250 22 7-9 l5 28 10-15 2O The following examples illustrate butdo not limit the invention. Example 1 A cylindrical high-tensile steeltube, 11A; inches internal diameter, 1% inches external diameter, 20inches long and closed at one end, is charged with 200 gm. of a mixtureof sodium nitrite and ammonium chloride, granulated 24-100 mesh,containing 1.5% light magnesium oxide as stabiliser. A suitable igniter,such as a 30-grain powder fuze or a safety igniter, is embedded in thecharge, and the leads are brought forward through the open end of thetube. The charge occupies approximately 11 inches of the tube. Theremainder of the tube up to 2 inches from the mouth is filled with sand,well shaken down but not rammed hard. A plug of plaster of Paris is thencast into the remaining two-inch space at the open end of the tube,which is provided with grooves or holes to assist in keying the plasterof Paris plug to theV tube. When initiated in `the usual manner, thecharge vents-at an internal pressure of approximately 9 tons per squareinch; and when the device is well tamped in a borehole, a satisfactoryblasting effect is obtainable.

Example 2 A tube 29 inches long is charged with 300 gms. of a mixture asin Example 1. The tamping consists of 12 inches of dry sand and a 2 inchAplaster 0I Paris plug. The means of initiation is a safety igniter ofthe type described in copending application Serial No. 758,317, ledJanuary 19, 1934, situated at the base of the tube. When initiated, thecharge vents at a pressure of 16 tons per square inch.

A type of pressure-resistant container suitable for use according to theinvention is a plain cylindrical steel tube closed at one end and ifdesired otherwise free from constructions, screwed fittings, or anyother device likely to ,prevent free egress of the contents of the tube.Tubes open at both ends, and having the charge placed more or lessevenly between two columns of granular packing material and two sealingplugs, may also be used: but the single-open-.end tube is preferred.

Another suitable type of container is a cylindrical steel tubehemispherically closed at both ends and provided with lateral ventingapertures near one end. In a device of this kind the blast does notproduce such a reaction tending to cause the tube to be moved in anaxial direction as may ,happen when a simple open-ended tube is used.

As charges I may use the gas-producing compositions described andclaimed in U. S. Patents 2,038,772, 712,052, 2,048,827, copendingapplications Serial Nos. 68,143? and 96,121, led March 10, 1936, andAugust 14, 1936, respectively, and in co-pending application Serial-No.162,221, filed September 2, 1937; or any other suitable compositionhaving the properties described.. The lnvention is best applied however,when used with charges that do not produce a blasting effect,l

when used under comparable borehole conditions, except when contained ina pressure-resistant enclosure adapted to confine the products' of theirdecomposition during its initial stages.

As means of initiating the charges I may use electrically-fired powderfuzes or detonators, or safety igniters.

Thepacking material used is preferably sand, or a similar material, theessential property being that it must pack" under the application ofrapa plug of plaster of Paris, castinto place; but an oversize wooden orlike plug driven into the mouth of the tube will a1so serve, althoughits resistance is more diicult torgauge. When using seals cast intoplace, I prefer to use sealing materials that expand on solidication, ofwhich'.`

plaster of- Paris is the most convenient. The seal may be, if desired,formed afterthe device has been loaded in the borehole, for example bysoaking the granular tamping at the mouth of the tube With Water andtamping the borehole next to the tube with solid carbon dioxide so that`a plug of ice is formed.

This invention is useful in the art as it provides new and 'effectiveblasting devices which are easy and economical to make.

Certain blasting devices constructed according to the invention are safeforuse in ery and gassy mines, and may even be vassembled, with` safetyat the working face.

For example, devices of the foregoing type vmay and provided with aninitiating device of thev twype described in co-pending applicationSerial As manyapparently Widely different embodi- Y ments of thisinvention may be made without departing from the spirit and scopethereof it is to be understood that I do not limit myself to the devicecomprising a non-destructible re-usable pressure-resistant container, acharge of nondetonating gas-producing material disposed in saidcontainer, igniting means disposed adjacent to said charge, ventingmeans confining said charge in said container comprising a column ofinert granular 'material and a supporting member located in the end ofsaid contaner adjacent to said inert granular material.

2. A non-detonating gas-generating blasting device comprising anon-destructible re-usable pressure-resistant container, a charge ofnondetonating gas-producing material disposed in said container,igniting means disposed adjacent to said charge, venting means confiningsaid charge in said container comprising a column of inert granularvmaterial and a cast plug of material having the property of expansionon solidication disposed in the end'oi said container and supportingsaid column of inert granular material.

,3.A non-detonating gas-generating blasting device comprising anon-destructible re-usable pressure-resistant container, a charge ofnondetonating gas-producing Ymaterial disposed.- in

said container, igniting means disposed adjacent to said charge, ventingmeans confining said charge in said container comprising a column ofinert granular material and a plug of plasterv of Paris cast into placein the venting end of said container supporting said column of inertgranular material..

4. A non-detonating gas-generating blasting device comprising anon-destructible re-usable pressure-resistant' container, a charge ofnondetonating gas-producing material disposed in said container,igniting means disposed adjacent' to said charge, venting meansconfining said charge in said container comprising a column of sand anda plug member disposed in the end of said container suuporting saidsand.

5. A non-detonating gas-generating blasting device .comprising are-usable*pressure-resistant container consisting of a cylindrical steeltube closed at one end, a charge of non-detonating gas-producingmaterial disposed Within said tube adjacent to the closed end thereof,an igniter embodied in said charge, a column ofsandfdisposed in saidtube between the locus of said charge and the opened end of said tube,keying means in the mouth of said tube, and a plug of plaster of Pariscast into place closing saidmouth and co-operating with said keyingmeans.

JAMES TAYLOR.

